This invention relates generally to a cell device, in particular to a chemical cell device having a positive electrode, a negative electrode, and an electrolyte, capable of generating electricity through chemical reactions, also capable of electrically charging and discharging.
A chemical cell device usually includes a positive electrode and a negative electrode each comprising an active material capable of electrically charging or discharging by collecting or producing electrons, an amount of electrolyte allowing smooth flowing of electric current and constituting another place for electrically charging and discharging by adjusting the amount of ions in the electrolyte, and a porous insulating separator provided to prevent short circuit possibly occurring between the positive electrode and the negative electrode, but not to impede ion conductivity in the electrolyte.
FIG. 3 is a cross sectional view illustrating a chemical cell device of prior art. As shown in FIG. 3, the conventional chemical cell device comprises: a positive electrode formed by depositting an active material layer 103 on a current collecting material 101, a negative electrode formed by depositting another active material layer 104 on another current collecting material 102, a porous insulating separator 105 for separating the positive electrode from the negative electrode. Referring to FIG. 3, the positive electrode, the negative electrode and the separator 105 are fixed together by means of a gasket 107 so as to form a sealed package filled with an amount of electrolyte 106. In practice, the porous insulating separator 105 is made of a porous insulator material, serving to separate the positive electrode active material layer 103 from the negative electrode active material layer 104, but not to impede ion conductivity in the electrolyte. By adjusting the amount of ions in the electrolyte, the positive electrode active material layer 103 and the negative electrode active material layer 104 may accumulate electric charges and perform discharge, allowing smooth flowing of electric charges to the positive electrode current collecting material 101 and the negative electrode current collecting material 102, thus causing the two electrodes to have different electric potential and thereby forming a desired chemical cell device.
In the layer-built chemical cell device shown in FIG. 3, the positive electrode active material layer 103 and the negative electrode active material layer 104 together provide an electric conductance, the value of which depends on the mass of these electrode active material layers 103 and 104. In order to obtain an increased conductance for a chemical cell so as to achieve a large electric current within the chemical cell during electric charging and discharging, it is required that the positive electrode active material layer 103 and the negative electrode active material layer 104 should have either large areas or great thicknesses.
Further, since charge and discharge of a chemical cell are usually effected through intercalation/deintercalation of ions between the active material layers and the electrolyte interface, there is an ion concentrate gradient from the surface of the active material layers to the inmost portions thereof. On the other hand, since it is considered that the surfaces of active material layers contribute greatly to the charging and discharging of a chemical cell, it is necessary to have a large contact area between the active material layers and the electrolyte (even if the mass of active materials remain unchanged) so as to increase the efficiency for electric charging and discharging.
In recent years, with the development of various electronic instruments using chemical cells, there has been a requirement for some improved and broadly usable chemical cell devices which are compact in size, high in capacity, and have a highly stable charging/discharging efficiency not depending upon an ambient temperature.
In order to meet the above requirement, an improved chemical cell device shown in FIG. 4 has been suggested which is constructed such that its positive electrode active material layer and its negative electrode active material layer have greatly increased areas, thus ensuring a desirably large capacity for electric charging and discharging.
However as shown in FIG. 4, when the positive electrode active material layers 103 and the negative electrode active material layers 104 have their areas increased, the chemical cell itself will become too large in size. In manufacturing the chemical cell shown in FIG. 4, the positive electrode (including the positive electrode current collecting material 101 and the positive electrode active material layers 103) and the negative electrode (including the negative electrode current collecting material 102 and the negative electrode active material layers 104) are rolled up together into a generally cylindrical form with the separators 105 interposed therebetween as shown in FIG. 4. Then, the rolled-up materials are sealed into a package filled with an electrolyte, thus forming a chemical cell device. But, in the structure of a chemical cell shown in FIG. 4, it is difficult to increase the thickness of the electrode active material layers 103 and 104 due to a restriction in the size of a chemical cell. As a result, it is impossible to ensure a sufficiently large cell capacity. In other words, if the thickness of the electrode active material layers 103 and 104 are increased in order to ensure a sufficiently large cell capacity, the chemical cell device will become too large in its overall size and this is not desirable.
Moreover, the chemical cells shown in FIGS. 3 and 4 have a common problem that the charging/discharging efficiency will depend to a great extent on an ambient temperature. For instance, the charging efficiency will become extremely bad when the ambient temperature is very low, causing unstabilized operation of the chemical cell device.